Ethernet: moving to field level

01 November 2021

We find out from the ODVA how Ethernet is cost-effectively traversing the last mile to field devices in industrial applications.

Control applications in industrial segments were traditionally enabled by pneumatic signals created using varied air pressure resulting in communication and motion. This was followed by analogue electrical signals where levels of current on a continuum, such as 4-20 milliamps, were interpreted as different process values or control actions. 

The next major evolution – fieldbus communication – provided half-duplex serial transmission via a digital data signal that is transmitted one bit at a time in sequence, allowing for much greater breadth of control, process variable communication, and diagnostics. 

The most recent advance in automation is Ethernet communication, allowing for full-duplex communication with complex data packets, enabling more information to be transmitted more quickly than ever before. The higher complexity and cost of early Ethernet iterations initially kept this technology limited to functioning as a higher network level communication backbone. Today, however, new standards such as Single Pair Ethernet (SPE) and Ethernet-APL are making it possible for Ethernet to traverse the last mile to field devices in a cost-effective manner in order to create a more seamless and powerful automation network. 

This next step in the use of Ethernet will bring valuable benefits end users have long awaited that will help power the Industry 4.0 revolution.

Technology availability 
Ethernet-APL is a new two-wire, intrinsically-safe physical layer that is suitable for use in demanding process automation applications. Ethernet-APL is made up of SPE (IEEE 802.3cg-2019, 10BASE-T1L), engineered power, Intrinsic Safety (IEC 60079, 2-WISE), and Type A fieldbus cable (IEC 61158-2, for intrinsic safety). Ethernet-APL enables up to 1,000m per trunk length and dramatically increased speed at 10 Mbit/sec. As it is just a physical layer, Ethernet-APL allows end users to access standard safety and security services built on IEC 61508 and ISA/IEC 62443 from the leading industrial automation standards bodies. Additionally, Ethernet-APL is able to support EtherNet/IP, HART-IP, OPC UA, PROFINET, or any other higher-level network protocol. 

Ethernet-APL technology is now available including the release of specifications, engineering guideline, and conformance test plans. Port profiles have also been defined that create the Ethernet-APL concept for multiple power levels with and without Instrinsic Safety hazardous area protections. 

In-cabinet resource-constrained devices 
EtherNet/IP in-cabinet resource-constrained device support is a significant technological advancement that utilises SPE to bring Ethernet to low-level in-cabinet devices such as contactors and push buttons. Limitations including cost, available space, and power consumption have resulted in many edge devices remaining hardwired. However, this lack of network connectivity results in time consuming installation, challenging troubleshooting, and a lack of diagnostic information. The steady decline in the cost and size of semiconductor chips, combined with the availability of SPE has enabled an EtherNet/IP in-cabinet bus solution which uses a multidrop network and control power cable that spans a single cabinet with one interface per device and one switch port across multiple devices to reduce both commissioning and hardware cost. 

EtherNet/IP for in-cabinet resource-constrained devices will enable the benefits of additional diagnostics, asset information and parameterisation capability, automatic node topology discovery, and plug and play device replacement compared to existing hard-wired devices. SPE will enable the use of one seamless EtherNet/IP network for both constrained and non-constrained devices. 

CIP Security 
In addition to the expansion of EtherNet/IP for in-cabinet solutions, CIP Security can now provide protections for resource-constrained devices including device authentication, a broad trust domain, device identity via Pre-Shared Keys (PSKs), and device integrity. Additionally, a narrow trust domain, user authentication, and policy enforcement are available options via a gateway or a proxy. Adding simpler devices to EtherNet/IP allows for the benefits of remote diagnostics, asset information, and parameterisation capability. The addition of more nodes to the network within the context of IT/OT convergence makes device level security critical to protect from physical harm and monetary loss.

New network opportunities 
SPE and Ethernet-APL driven enhancements broaden the range of Ethernet applications at the field level and provide a seamless experience for users. Building on this, expanded use of Ethernet in field devices will allow for a dramatic increase in both the amount of data as well as the speed with which it is transported enabling a host of new possibilities and benefits in existing automation applications. Faster commissioning can turn tasks that used to take minutes into seconds. Complex diagnostics access that enables easier and quicker device and system troubleshooting is another highly valuable benefit. Furthermore, additional processing power can elevate simple issue identification diagnostics to problem warning prognostics by analysing degradation of metrics such as pressure or signal quality relative to known proper operational boundaries.

Movement of large amounts of data can allow for processing either in an onsite edge computing appliance or via a remote cloud server to identify trends in order to increase operational output or to identify cost reduction opportunities. Further advances in Ethernet technology such as IEC/IEEE 60802 Time Sensitive Networking standards are enabling automation networks to simply and fairly share the wire both with each other as well as other communication traffic such as video that can be used for defect identification with machine learning or for security. In addition, all of the same safety and security benefits from previous technologies are possible, albeit in different and oftentimes improved ways. In summary, Ethernet offers new possibilities including enhanced remote commissioning, asset management, control, analytics, and diagnostics/prognostics, which will help continue to drive adoption at the field level. 

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